Optical fabric analyzer



Jan. 20, 1959 F. NIEMAN 121-5 5 OPTICAL FABRIC ANAL Y ZER Filed April 14, 1955 3 Sheets-Sheet 1 INVENTORS William J. Han

Donqld F. Niemun ATTORNEYS Jan. 20, 1959 D. F. NIEMAN ET AL 2,869,416

OPTICAL FABRIC ANALYZER Filed April 14, 1955 5 Sheets-Sheet 2 FIG. 2

INVENTORS William J. Han Donald F. Niemun BY 229.941

ATTORNEYS Jan. 20, 1959 D. F. NIEMAN ET AL 2,859,416

. OPTICAL FABRIC ANALYZER Filed April 14, 1955 3Sheets-Sheet :5

FIG. 3

30d 0 3of 30h Intensity Length of S pecimen FIG. 4

48 I To Recorder I NVENTORS.

William J. Hart BY Donald F. Niemon w Ta- ATTORNEYS United States PatentO OPTICAL FABRIC ANALYZER Donald F. Nieman, Charlottesville, Va., and William J. Hart, Dalton, Pa., assignors to Institute of Textile Technology, Charlottesville, Va., a corporation of Virginia Application April 14, 1955, Serial No. 501,324

Claims. (Cl. 88-14) This invention relates to instruments for the precision analysis of the characteristics and defects of fabrics.

A fabric woven or knitted from natural or artificial fibres is a structure of great complexity. Some of the factors which determine the all important appearance of the fabric are the geometrical and physical characteristics of the yarn, such as its diameter, twist, loftiness, count, fibre blend and so forth, and the geometrical and physical characteristics of the fabric structure formed from the yarn, such as reed and dent marks and the spacing and lay of the yarns, solid content, uniformity of finishing, such as the manner in which the yarn absorbs dye, resin and other finishes, and uniformity of gloss or lustre. While this does not constitute a comprehensive recital of the factors contributing to the final appearance of a fabric, the great majority of defects in the appearance to the unaided eye of finished fabrics can be traced to variations in the characteristics enumerated above. Moreover, such tangible qualities of a fabric as its handle, drape and comfort are dependent to a large degree on the geometry of a fabric and of the yarn of which the fabric is comprised.

Prior to our present invention, certain apparatus has been described in the literature which is adapted to analyze a particular kind of defect in textile fabrics; This apparatus is called a streakmete r and is described in an article by H. F. Hume, E. H. Olson and C. E. Reese: Characterization of Warp Streaks in Woven Fabrics- Development and Use of the Streakmeter which appeared'in the Textile Research Journal, vol. XXIII, Feb. 1953. However, there has been no instrument available which is capable of making precise analytical studies of the characteristics of fabric structures to enable manufacturers to undertake a rational and systematic approach to the improvement of fabrics generally and to enable them to determine the precise nature of an. apparent defect in a particular fabric in order that the defect may be traced to its origin and remedied in a logical and orderly manner.

-We have invented a novel and useful optical instrument for the analysis of the characteristic features of fabric structures. Our new instrument makes possible a logical and precise evaluation of the several factors contributing to the overall quality and appearance of fabric structures and the determination of the exact nature of variations in these factors which contribute to defective quality and appearance of improperly constituted'fabrics. According to our invention, we provide, in conjunction with means for mounting a fabric specimen to be analyzed, a specimen illuminating means including a source of light and a first optical system adapted to concentrate light on a portion of the specimen to be analyzed. We also" provide alight sensitive means and a second optical system adapted to project on the sensitive means the light emanating by reflection from or transmission through the fabric specimen undergoing analysis. The mounting for the fabric specimen under analysis includes means "ice adapted to translate and rotate the mounting in a manner such that an elemental area in the plane of the specimen is always in a focal plane of the second optical system. Means are also provided which permit illumination of the specimen over a broad range of angles of incidence and which also make possible the examination of the specimen either by transmitted or reflected light emanating from the specimen over a broad range of angles.

Wherever we refer to light, light sources, light filters, light sensitive means and other optical components, it is to be understood that we mean light as radiant energy in the ordinary optical region including ultra-violet and infra-red light such as used in fluorescence and trapped fluorescence studies; we do not intend that our invention be restricted to the use of light in the visible spectrum.

An outstanding feature of our invention is the means for the precision measurement of optical and geometric properties of fabric structures and the nature of variations in the characteristics of such structures. The uti-. lization of certain accessories with the basic embodiment of our invention makes possible kinds of optical and geometric measurements not heretofore obtainable with fabric analyzing instruments known in the art. For a complete description of one embodiment of our invention, attention is directed to the following detailed description and the accompanying drawings in which:

Fig. l is a perspective view of apparatus constituting a fabric analyzer according to our invention;

Fig. 2 is a schematic plan view of the apparatus of Fig. 1 illustrative of the operation thereof;

Fig. 3 is a typicalrecorder chart obtained with theapparatus of Figs. 1 and 2; and

Fig. 4 is a schematic representation of a. modification of the apparatus of Fig. 1.

Referring now to Fig. l, a specimen mount 1 comprises a frame 2 in which a sample of fabric 3 may be stretched. The mount is adapted to be rotated about the vertical axis indicated at 4 and to be reversibly translated at a uniform rate in a plane containing the axis 4. Translation of the frame 2 is accomplished by a precision Worm gear and collar within the housing 5, the worm being reversibly driven by a suitable motor 6 mounted on a fixed sleeve 7. The collar on the Worm is fixed to the mount so that as the collar travels in either direction along the length of the Worm, the mount is translated in either of the directions indicated by the arrows. These directions are radial of the axis 4.

The housing 5 for the translating mechanism is mounted'on a shaft 8 and may be rotatably driven in either of the directions indicated by the arrows by a suitable reversible motor 10. The operation of the motors 6 and 10 may be coordinated, if desired, so that related and simultaneous rotation and translation of the specimen mount is afforded.

Illumination of the specimen is effected by illuminating means 11 which is mounted at one end of an arm 12,

the other end of the arm being fixed to a rotatable col-- lar 13 about the shaft 8. This illuminating means is,

provided with a light source 14, a suitable optical sysing the illuminating means 11 permits orientation of the light source 14 over a wide range of angles of reflectance.

or transmission with respect to the fabric specimen 3 as is illustrated by the illuminating means indicated in phantom at 11'. For precision determination of the angle of incidence of light projected on the specimen, a protractor 18 is provided in cooperative relation with the arm 12 carrying the illuminating means 11.

Light transmitted by or reflected fromv the. specimen 3 being analyzed is transmittedv by, a second. optical system 20 and projected. through appropriate. filters or. polariz'ers indicated generally at. 21..' The filtered. or. polarized'light is then focuseduponan. elongated slit.22. which serves to mask oif'alloflthe. imagev being analyzedexcept. that of an elongated elementalrarea offthe specimen, which area includes the, axis. 4. The arrangement of'the translating and'rotating components of the speci+ men mountis such that the imageof, this elementalarea of the specimen 3' under examinationalwayslies. in-the: fccalplaneoffthe optical system20, .whatever theorientation of the specimen as a Whole,

The light of the masked image passing through. the slit 22 falls on a photoelectric, cell 23. The signalcurrent excited'therein is amplified by an amplifier 24 of any suitable type. This amplified'signal representative of the light intensity of the masked image is. then fed to a recorder 25 which comprises a timed driving mechanism for a chart and. a marking pen which is actuated. in response, to. the incoming signals from the amplifier 24. This recorder is a conventional direct inking recording milliarnmeter and is provided with a chart having suitable. scales printed thereon.

A particularly useful form of the optical'systemlill incorporates .a cylindrical, rather than a spherical, lens, the gec'mctricaxis of the cylindrical lens being oriented. parallel to the axis 4 andto the length of'the elongated slit22; It'willbe understood that the fabric specimen is generally positioned in the frame 2 so that eitherthe warp or woof threads are parallel to the lengthlof' the slit 22.v Thus, where a cylindrical'lens is employed, a longer; undistorted image of a thread isobtainable. We have also foundthat in our improved fabric analyzer the use-of a cylindricallens in cooperation with the slit and photocell effects better resolutionof the fabric in this longer image and. an averaging of the illumination reflected from or transmitted. through the longer area of' fabric-under observation which, in turn, provides .a more. meaningful indication of the characteristics of that area. than is obtained with a spherical lens. The latter type. of lens-gives a' useful image of a lesser length of the fabric which results in an indication of the characteristics. of a more specific area of the fabric. However, such an indication is not generally as significant as is one of an average intensity of light reflected by or. transmitted from a more extensive length of fabric. or yarn so. far. as appearance'of the fabric to the unaided'eye is con: cerned.

The optical fabric analyzer just'described iscapable of making two basic kinds of measurements: (a) Reflectance, transmittance and fluorescence measurements; and-(b) gloss and lustre measurements.

To illustrate the first category of-measurements; our fabric analyzer is set up as follows:

The fabric specimen to be analyzed is rnounted'in the frame 2 with the warp or woof yarns to be studied. placed parallel to the axis 4, in which orientation they are also parallel to the long dimensionof-the slit 22,. as previouslystated. The illuminating meansjlliispositioned'as at 11' to illuminate the specimen atsome desired'angle of incidence, and the optical system 20 'is focused on the illuminated area. The motor-6 is then started to cause the mounting frame 2 to traverse. It

is now seen that, as the fabricspecimen traverses the field of the optical system 20, the light image focused on the photoelectric cell 23 through the slit 22 will alternately'be'that representative of successive yarns 'of the speci-v men and of the spaces between the yarns. When the image: is obtained from light reflected from the-surface of-the specimen, the yarns themselves; are represented by relativcly "bright portions of the image focused on traversal of the mounting frame.

the photoelectric cell and the spaces are represented by relatively dark portions. The photoelectric cell is excited accordingly and the signal current is passed through the amplifier 24 to the recorder 25 to actuate the tracing pen therein as the chart advances at a rate related to the speed of traverse of the specimen. The speed of the recorder chart can bear any desired ratio to the speed of The result is a sinuous trace onthe recorder chart 26 representative of the varying intensities of, light reflected from the yarns andspaces of the specimen as registered .by the photoelectric cell. It is readily apparent that such a curve, although complex,

' furnishes much information about fabric structure which cannot bedetermined by instruments heretofore known in the art. It canbe stated that. a curve of the kind made with this instrument, except where the curve is the result of a study of a single thread or yarn, will generally be quadrifunctional, i..e. it will. be a function of the following, variables:

(a) Optical variationof yarns,

(b) O'ptical variation ofinteryarn spacing;

(c)'- Dimensionalvariations of yarns, and I (d) Dimensional variations ofinteryarn spacing.

the images of theyarns willrappear as relatively'dark areas,v

and the; spacesibetween adjacentyarns will appear as light: areas; The-:photoelectric; cell 23 willrespond to the alternately light and darkimages as before. andcause the: recorder: totrace a sinuous curve representing the:

' intensity of;light;transmitted through the fabric-at'successive positions along it. Such a. curvemay be analyzed for irregularities indicative of defects inrthe'structure of the. fabric specimen.

In Fig; .3 there:is.shown atypical chart obtainedfrom a defective: fab'ricispecimen. In this instance the chart was made withtlight'transmitted through the fabric and therefore the; peaks 27 represent,.in.suitable'units-.indi cated on. the scale.at:the left-hand end ofthe-chart, the light transmissionof the spaces. between adjacent'yarnswhile;the.valleys 28 represent the intensitiesofthe light transmitted through theyarnsthemselves. For purposes ofanalysis we also establish, with the aid of the scale, themid-points 30 betweenadjacent maximum. and minimum transmission levels.

This curve, shownin Fig. 3; may beanalyzedinto functions whichyield. measures: of yarn diameter, spacing-v diameter; opticaltransmission of yarns, and optical trans-- mission of spaces. Moreover, av curve made with reflected: light, rather thanv transmitted light, mayalso be analyzed into functionsindicative of yarn reflectance and spacing reflectance; As will be: apparent toione skilled inthe textile: art,.the particular fabric from which the curve is taken willalmost alwayszinfluence'the characteri'sticsofthe curve; that is to' say," the derived functions .of transmission andreflectance, for example, will beamodified :in some. degreeby the-amount of fuzz, the yarn diameter, and the rectilinearity of the particular yarn and its spacing withrespectto adjacent yarns. However, from information of the kind which can be derived much can .be. known about the nature ofa correctlyformed fabric structure; and the. nature andlocation. of defects. canbetexactly .determined-so that thecauses thereofmay be.v corrected...

Gloss orluster of a fabric mayrbe analyzed'b'y our new device. Specifically, there are at least two techniques to which our analyzer is adapted. One of these is the goniophotometric"measurement of a single yarn or of a single elemental area. Our analyzer makes such a measurement by automatically recording the reflectance values at different specular angles, i. e. viewing angles, with respect to the fabric specimen, which angles may vary from grazing incidence to normal to the plane of the fabric. For this purpose the arm 12 carrying the light source 11 is linked to the specimen carriage housing 5. This linkage sets the angle of illumination at some fixed value. The motor then rotates the linked assemblies 11 and 5 about the axis 4 which effects a continuing change of the angle between the line of observation of the fabric surface and the plane of the surface itself. The changing intensity of light reflected from the surface of the fabric through the optical system 21 and the slit 22 onto the photoelectric cell 23 produces a varying signal which is amplified by the amplifier 24 to drive the recorder 25. The varying intensity of this reflected light is represented by a graph of varying amplitude on the recorder chart which is a plot of reflectance with respect to the angle of observation. This graph may be analyzed or interpreted as is customary with goniophotometric observations.

Another type of relative gloss or lustre measurement may be made with our new analyzer if two sensing elements or photoelectric cells are used instead of the single one indicated at 23 in Fig. 1. This arrangement is shown in Fig. 4. Here one of the photoelectric cells 31, its cooperating optical system 32 and masking slit 33 are arranged to sense light reflected normally from the surface of the fabric specimen 3 in the frame 2 while the second photoelectric cell 34 and its optical system 35 and masking slit 36 are arranged to sense light reflected at any desired specular angle with respect to the fabric surface. Of course, at any particular instant both optical systems 32 and 35 must be focused on the same yarn or area of the fabric specimen under analysis. With the light source 11 set to illuminatethe fabric specimen at some fixed angle with respect to the surface thereof, the specimen frame 2 is now caused to traverse the fabric across the fields of the optical systems for the two photoelectric cells by the same means as described in connection with Figs. 1 and 2, and the responses of the two cells are recorded as before.

While the light intensities at the two angles of observationmay be recorded separately and the charts compared to determine the relative gloss of the fabric specimen at the two angles of observation, we prefer the embodiment of Fig. 4 in which the comparison is automatically expressed as a single function on a recorder chart. In

this modification the signals from the photoelectric cells are separately amplified by amplifiers 37 and 38 and are then impressed on a potentiometer 39 as shown in Fig. 4. In this circuit the output of amplifier 38 is connected to the potentiometer terminal 40 while the output of the amplifier 37 is connected to the potentiometer terminal 41. This latter terminal is the variable tap and is mechanically coupled by any suitable means indicated at 42 to the rotor 43 of a suitable servomotor 44 adapted to keep the potentiometer in balance at all times regardless of variations in the signals applied at the terminals 40 and 41.

Now, any null position of the movable tap 41 of the potentiometer 39 becomes, when appropriately calibrated,

a measure of the relative intensities of the light reflected from the fabric specimen onto the two photoelectric cells. For example, if the intensity of reflected light sensed by cell 34 is twicethe intensity of light sensed by cell 31, the output signals of amplifiers 38 and 37 will have a ratio of 2:1 which will cause the mp 41 to seek a null at the midway point of the potentiometer 39. This null position of tap 41 is further mechanically coupled as indicated at 45 to the variable tap 46 of potentiometer 47 connected across battery 48. The voltage at tap 46 in any position is related to the ratio of light intensities expressed by the corresponding positiOn 9; tap 41 and is utilized to drive a suitable direct inking recording milliam meter to produce a graph representative of the relative variations of gloss at successive positions along the length of the fabric specimen under analysis. Depending on the intended appearance of the fabric specimen, regularity or irregularity in the variation of gloss as indicated by the recorder chart will be indicative of normal or abnormal appearance of the fabric. In any event, a particular value of gloss indicated on the recorder chart may be related exactly to that portion of the fabric specimen having that gloss. If this particular value is abnormal and is indicative of a defect in the fabric structure, the defective portion of the specimen is easily located and the causes of the defect may be readily traced to the step in the manufacture of the fabric or yarn which caused the defect.

The addition of certain optical accessories greatly increases the versatility of our new optical fabric analyzer. For example, if narrow band optical filters are utilized at 17 or 21, the transmittance and reflectance characteristics of fabrics may be studied at different wave lengths of light. Also, polarizing elements :inserted at 16 or 17 permit the study of dichroism of fibres and fabrics as well as of transmittance and reflectance characteristics of fabrics by polarized light. For some applications it is also useful to utilize an ultraviolet or infrared light source at,14.

From the foregoing it is seen that our new fabric analyzer is an extremely valuable and versatile tool in the control of fabric manufacturing processes. it features means for the accurate dimensional measurement and location of the structural elements of fabrics, such as yarn diameter and interyarn spacing. No instrument of this kind in the prior art has such a feature. Furthermore, means are provided for illumination'of the fabric specimen over'a wide range of angles to permit analysis thereof under both reflected and transmitted light. In addition, the specimen frame and drive assembly is rotatable through an arc of nearly degrees. This flexi: bility in our new instrument permits viewing the specimen over a broad range of angles. This variable viewing angle makes possible goniophotometric studies which cannot be made with instruments previously known.

Many variations and modifications of the embodiment of our invention described above are possible and we do not propose to be limited to the exact details set forth. The scope of our invention is defined in the subjoined claims.

We claim: I

1. Apparatus for analyzing woven fabric by detecting variations in the intensity of light transmitted through or reflected from elemental areas of the fabric, which apparatus comprises a specimen carriage, means for mounting said carriage for rotation about an axis, a frame for plane mounting of a fabric specimen to be analyzed, means for movabiy mounting said frame on said carriage such that the axis of rotation of the carriage always lies in the specimen plane and the frame moves on the carriage radially of the carriage axis, specimen illuminating means mounted for revolution through an arc of more than 180 about the axis of rotation of the carriage, said illuminating means including a light source and a first optical system for projectihg light onto the area of the specimen frame in which the carriage axis lies, a first light sensitive means and a second optical system adapted to project on said light sensitive means light emanating by transmission through or reflection from an elemental area of the specimen frame in which the carriage axis lies, and means responsive to said light sensitive means for detecting the variations in intensity of the light projected thereon.

2. Apparatus according to claim 1 in which said second optical system comprises a cylindrical optical element having its geometrical axis parallel to the axis of said carriage, said optical element being focused on the clo mental area of the specimen plane of said frame in which the carriage axis lies.

'3. Apparatus for analyzing fabric by detecting variations in theintensity of light transmitted'through or refiected from elemental areas of the fabric, which apparatus comprises a specimen frame for'planemounting of a fabricspecime'n; a shaft mounted for rotation about itsaxis, a frame carriage fixed to said shaft and extending normal to the shaft axis, means on said carriage for moving said frame radially of the shaft axis such that the axis always lies in the specimen plane of the frame, specimen illuminating means mounted for revolution through an arc of more'than 18'0" about the axis ofrotation of the carriage, saidilluminating-means including a light sourceand a first optical system for-projecting light onto the area of the specimen frame in which the shaft axis lies, a first light sensitive means and second optical system adapted to project on said light sensitive means 4. Apparatus according to claim 3 in which said second optical system comprises at least one cylindrical optical element having its geometrical axis parallel to the axisof said shaft, said optical element being positioned with' respect to said specimen and said sensitive means such that only the light emanating from the elemental area of the specimen plane of said frame in which the carriage axis lies is projected on said light sensitive means:

5. Apparatus according to claim 3 which further corn prises means for rotating said'shaft and means'for'coordinating the rotation of said shaft and the revolution ofsaid illuminating means.

6. Apparatus according to claim 3 in which saidspeci men illuminating means further comprises an arm-extending radially from the axis of said shaft and mountedat one end for revolution about said axis, said lightsourcebeing mounted on the end of said arm remote from said shaft and said first optical system being mounted on-said' arm between said source and said shaft.

7. Apparatus according to claim 6 which further'comprises means for coordinating the rotation of said arm I about said shaft and the ro-tation of said shaft, whereby apredetermined angle of illumination of a specimen may be maintained as the plane of the specimen is rotated about the axis of the shaft.

8. Apparatus according to claim 1 which further comprises a second light sensitive means and a third optical systemwhich is displaced about'the carriage'axis' from said-second optical system, sa'idthirdoptical sy's'tcmbei-ng adapted to project on'said second light'sensitivemeans' light emanating from the specimena't a different anglefrom the angle at which the light projected by said-second optical system emanates from the specimen, second'meanscylindrical optical element, said optical element beingpositioned" with respect to-said'specimen and the associatedsensitive means such that only the light emanating from the elemental area of the specimen plane of'said frame in Which'the'carria'ge: axis lies is projected onsaid light sensitive means.

10. Apparatusaccording to claim 8 in which the means for comparing the responses of'saidfirst and second responsivevmeans' comprises an'output circuit connected'to said first and second light sensitive means, said-output-circuit'cornprising a potentiometer, the output of said first light sensitive means being connected to a fixed tap on said'potentiometer and the output of 'said'second sensitive meansbeingzconnectedto'a variable-tap cnsaid potentiometer; a 'servo'motor mechanically coupled to the variable:tapj of said potentiometer and having its control windings connected in said output circuit to maintain the potentiometer continuously in balance, means responsive to the position of the variable tap on said potentiometer for producing an output signal representative of the position ofthe-variable tap, and-a recorder responsive to said output si'gnal for producing a' graph of the variations thereof.

References Cited in the file of this patent UNITED STATES PATENTS 

